1.1 --- a/rt/emul/compact/src/main/java/java/lang/invoke/MethodHandle.java Sun Aug 17 20:09:05 2014 +0200
1.2 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000
1.3 @@ -1,1494 +0,0 @@
1.4 -/*
1.5 - * Copyright (c) 2008, 2013, Oracle and/or its affiliates. All rights reserved.
1.6 - * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 - *
1.8 - * This code is free software; you can redistribute it and/or modify it
1.9 - * under the terms of the GNU General Public License version 2 only, as
1.10 - * published by the Free Software Foundation. Oracle designates this
1.11 - * particular file as subject to the "Classpath" exception as provided
1.12 - * by Oracle in the LICENSE file that accompanied this code.
1.13 - *
1.14 - * This code is distributed in the hope that it will be useful, but WITHOUT
1.15 - * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.16 - * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.17 - * version 2 for more details (a copy is included in the LICENSE file that
1.18 - * accompanied this code).
1.19 - *
1.20 - * You should have received a copy of the GNU General Public License version
1.21 - * 2 along with this work; if not, write to the Free Software Foundation,
1.22 - * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.23 - *
1.24 - * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
1.25 - * or visit www.oracle.com if you need additional information or have any
1.26 - * questions.
1.27 - */
1.28 -
1.29 -package java.lang.invoke;
1.30 -
1.31 -
1.32 -import java.util.*;
1.33 -import sun.invoke.util.*;
1.34 -
1.35 -import static java.lang.invoke.MethodHandleStatics.*;
1.36 -import java.util.logging.Level;
1.37 -import java.util.logging.Logger;
1.38 -
1.39 -/**
1.40 - * A method handle is a typed, directly executable reference to an underlying method,
1.41 - * constructor, field, or similar low-level operation, with optional
1.42 - * transformations of arguments or return values.
1.43 - * These transformations are quite general, and include such patterns as
1.44 - * {@linkplain #asType conversion},
1.45 - * {@linkplain #bindTo insertion},
1.46 - * {@linkplain java.lang.invoke.MethodHandles#dropArguments deletion},
1.47 - * and {@linkplain java.lang.invoke.MethodHandles#filterArguments substitution}.
1.48 - *
1.49 - * <h1>Method handle contents</h1>
1.50 - * Method handles are dynamically and strongly typed according to their parameter and return types.
1.51 - * They are not distinguished by the name or the defining class of their underlying methods.
1.52 - * A method handle must be invoked using a symbolic type descriptor which matches
1.53 - * the method handle's own {@linkplain #type type descriptor}.
1.54 - * <p>
1.55 - * Every method handle reports its type descriptor via the {@link #type type} accessor.
1.56 - * This type descriptor is a {@link java.lang.invoke.MethodType MethodType} object,
1.57 - * whose structure is a series of classes, one of which is
1.58 - * the return type of the method (or {@code void.class} if none).
1.59 - * <p>
1.60 - * A method handle's type controls the types of invocations it accepts,
1.61 - * and the kinds of transformations that apply to it.
1.62 - * <p>
1.63 - * A method handle contains a pair of special invoker methods
1.64 - * called {@link #invokeExact invokeExact} and {@link #invoke invoke}.
1.65 - * Both invoker methods provide direct access to the method handle's
1.66 - * underlying method, constructor, field, or other operation,
1.67 - * as modified by transformations of arguments and return values.
1.68 - * Both invokers accept calls which exactly match the method handle's own type.
1.69 - * The plain, inexact invoker also accepts a range of other call types.
1.70 - * <p>
1.71 - * Method handles are immutable and have no visible state.
1.72 - * Of course, they can be bound to underlying methods or data which exhibit state.
1.73 - * With respect to the Java Memory Model, any method handle will behave
1.74 - * as if all of its (internal) fields are final variables. This means that any method
1.75 - * handle made visible to the application will always be fully formed.
1.76 - * This is true even if the method handle is published through a shared
1.77 - * variable in a data race.
1.78 - * <p>
1.79 - * Method handles cannot be subclassed by the user.
1.80 - * Implementations may (or may not) create internal subclasses of {@code MethodHandle}
1.81 - * which may be visible via the {@link java.lang.Object#getClass Object.getClass}
1.82 - * operation. The programmer should not draw conclusions about a method handle
1.83 - * from its specific class, as the method handle class hierarchy (if any)
1.84 - * may change from time to time or across implementations from different vendors.
1.85 - *
1.86 - * <h1>Method handle compilation</h1>
1.87 - * A Java method call expression naming {@code invokeExact} or {@code invoke}
1.88 - * can invoke a method handle from Java source code.
1.89 - * From the viewpoint of source code, these methods can take any arguments
1.90 - * and their result can be cast to any return type.
1.91 - * Formally this is accomplished by giving the invoker methods
1.92 - * {@code Object} return types and variable arity {@code Object} arguments,
1.93 - * but they have an additional quality called <em>signature polymorphism</em>
1.94 - * which connects this freedom of invocation directly to the JVM execution stack.
1.95 - * <p>
1.96 - * As is usual with virtual methods, source-level calls to {@code invokeExact}
1.97 - * and {@code invoke} compile to an {@code invokevirtual} instruction.
1.98 - * More unusually, the compiler must record the actual argument types,
1.99 - * and may not perform method invocation conversions on the arguments.
1.100 - * Instead, it must push them on the stack according to their own unconverted types.
1.101 - * The method handle object itself is pushed on the stack before the arguments.
1.102 - * The compiler then calls the method handle with a symbolic type descriptor which
1.103 - * describes the argument and return types.
1.104 - * <p>
1.105 - * To issue a complete symbolic type descriptor, the compiler must also determine
1.106 - * the return type. This is based on a cast on the method invocation expression,
1.107 - * if there is one, or else {@code Object} if the invocation is an expression
1.108 - * or else {@code void} if the invocation is a statement.
1.109 - * The cast may be to a primitive type (but not {@code void}).
1.110 - * <p>
1.111 - * As a corner case, an uncasted {@code null} argument is given
1.112 - * a symbolic type descriptor of {@code java.lang.Void}.
1.113 - * The ambiguity with the type {@code Void} is harmless, since there are no references of type
1.114 - * {@code Void} except the null reference.
1.115 - *
1.116 - * <h1>Method handle invocation</h1>
1.117 - * The first time a {@code invokevirtual} instruction is executed
1.118 - * it is linked, by symbolically resolving the names in the instruction
1.119 - * and verifying that the method call is statically legal.
1.120 - * This is true of calls to {@code invokeExact} and {@code invoke}.
1.121 - * In this case, the symbolic type descriptor emitted by the compiler is checked for
1.122 - * correct syntax and names it contains are resolved.
1.123 - * Thus, an {@code invokevirtual} instruction which invokes
1.124 - * a method handle will always link, as long
1.125 - * as the symbolic type descriptor is syntactically well-formed
1.126 - * and the types exist.
1.127 - * <p>
1.128 - * When the {@code invokevirtual} is executed after linking,
1.129 - * the receiving method handle's type is first checked by the JVM
1.130 - * to ensure that it matches the symbolic type descriptor.
1.131 - * If the type match fails, it means that the method which the
1.132 - * caller is invoking is not present on the individual
1.133 - * method handle being invoked.
1.134 - * <p>
1.135 - * In the case of {@code invokeExact}, the type descriptor of the invocation
1.136 - * (after resolving symbolic type names) must exactly match the method type
1.137 - * of the receiving method handle.
1.138 - * In the case of plain, inexact {@code invoke}, the resolved type descriptor
1.139 - * must be a valid argument to the receiver's {@link #asType asType} method.
1.140 - * Thus, plain {@code invoke} is more permissive than {@code invokeExact}.
1.141 - * <p>
1.142 - * After type matching, a call to {@code invokeExact} directly
1.143 - * and immediately invoke the method handle's underlying method
1.144 - * (or other behavior, as the case may be).
1.145 - * <p>
1.146 - * A call to plain {@code invoke} works the same as a call to
1.147 - * {@code invokeExact}, if the symbolic type descriptor specified by the caller
1.148 - * exactly matches the method handle's own type.
1.149 - * If there is a type mismatch, {@code invoke} attempts
1.150 - * to adjust the type of the receiving method handle,
1.151 - * as if by a call to {@link #asType asType},
1.152 - * to obtain an exactly invokable method handle {@code M2}.
1.153 - * This allows a more powerful negotiation of method type
1.154 - * between caller and callee.
1.155 - * <p>
1.156 - * (<em>Note:</em> The adjusted method handle {@code M2} is not directly observable,
1.157 - * and implementations are therefore not required to materialize it.)
1.158 - *
1.159 - * <h1>Invocation checking</h1>
1.160 - * In typical programs, method handle type matching will usually succeed.
1.161 - * But if a match fails, the JVM will throw a {@link WrongMethodTypeException},
1.162 - * either directly (in the case of {@code invokeExact}) or indirectly as if
1.163 - * by a failed call to {@code asType} (in the case of {@code invoke}).
1.164 - * <p>
1.165 - * Thus, a method type mismatch which might show up as a linkage error
1.166 - * in a statically typed program can show up as
1.167 - * a dynamic {@code WrongMethodTypeException}
1.168 - * in a program which uses method handles.
1.169 - * <p>
1.170 - * Because method types contain "live" {@code Class} objects,
1.171 - * method type matching takes into account both types names and class loaders.
1.172 - * Thus, even if a method handle {@code M} is created in one
1.173 - * class loader {@code L1} and used in another {@code L2},
1.174 - * method handle calls are type-safe, because the caller's symbolic type
1.175 - * descriptor, as resolved in {@code L2},
1.176 - * is matched against the original callee method's symbolic type descriptor,
1.177 - * as resolved in {@code L1}.
1.178 - * The resolution in {@code L1} happens when {@code M} is created
1.179 - * and its type is assigned, while the resolution in {@code L2} happens
1.180 - * when the {@code invokevirtual} instruction is linked.
1.181 - * <p>
1.182 - * Apart from the checking of type descriptors,
1.183 - * a method handle's capability to call its underlying method is unrestricted.
1.184 - * If a method handle is formed on a non-public method by a class
1.185 - * that has access to that method, the resulting handle can be used
1.186 - * in any place by any caller who receives a reference to it.
1.187 - * <p>
1.188 - * Unlike with the Core Reflection API, where access is checked every time
1.189 - * a reflective method is invoked,
1.190 - * method handle access checking is performed
1.191 - * <a href="MethodHandles.Lookup.html#access">when the method handle is created</a>.
1.192 - * In the case of {@code ldc} (see below), access checking is performed as part of linking
1.193 - * the constant pool entry underlying the constant method handle.
1.194 - * <p>
1.195 - * Thus, handles to non-public methods, or to methods in non-public classes,
1.196 - * should generally be kept secret.
1.197 - * They should not be passed to untrusted code unless their use from
1.198 - * the untrusted code would be harmless.
1.199 - *
1.200 - * <h1>Method handle creation</h1>
1.201 - * Java code can create a method handle that directly accesses
1.202 - * any method, constructor, or field that is accessible to that code.
1.203 - * This is done via a reflective, capability-based API called
1.204 - * {@link java.lang.invoke.MethodHandles.Lookup MethodHandles.Lookup}
1.205 - * For example, a static method handle can be obtained
1.206 - * from {@link java.lang.invoke.MethodHandles.Lookup#findStatic Lookup.findStatic}.
1.207 - * There are also conversion methods from Core Reflection API objects,
1.208 - * such as {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect}.
1.209 - * <p>
1.210 - * Like classes and strings, method handles that correspond to accessible
1.211 - * fields, methods, and constructors can also be represented directly
1.212 - * in a class file's constant pool as constants to be loaded by {@code ldc} bytecodes.
1.213 - * A new type of constant pool entry, {@code CONSTANT_MethodHandle},
1.214 - * refers directly to an associated {@code CONSTANT_Methodref},
1.215 - * {@code CONSTANT_InterfaceMethodref}, or {@code CONSTANT_Fieldref}
1.216 - * constant pool entry.
1.217 - * (For full details on method handle constants,
1.218 - * see sections 4.4.8 and 5.4.3.5 of the Java Virtual Machine Specification.)
1.219 - * <p>
1.220 - * Method handles produced by lookups or constant loads from methods or
1.221 - * constructors with the variable arity modifier bit ({@code 0x0080})
1.222 - * have a corresponding variable arity, as if they were defined with
1.223 - * the help of {@link #asVarargsCollector asVarargsCollector}.
1.224 - * <p>
1.225 - * A method reference may refer either to a static or non-static method.
1.226 - * In the non-static case, the method handle type includes an explicit
1.227 - * receiver argument, prepended before any other arguments.
1.228 - * In the method handle's type, the initial receiver argument is typed
1.229 - * according to the class under which the method was initially requested.
1.230 - * (E.g., if a non-static method handle is obtained via {@code ldc},
1.231 - * the type of the receiver is the class named in the constant pool entry.)
1.232 - * <p>
1.233 - * Method handle constants are subject to the same link-time access checks
1.234 - * their corresponding bytecode instructions, and the {@code ldc} instruction
1.235 - * will throw corresponding linkage errors if the bytecode behaviors would
1.236 - * throw such errors.
1.237 - * <p>
1.238 - * As a corollary of this, access to protected members is restricted
1.239 - * to receivers only of the accessing class, or one of its subclasses,
1.240 - * and the accessing class must in turn be a subclass (or package sibling)
1.241 - * of the protected member's defining class.
1.242 - * If a method reference refers to a protected non-static method or field
1.243 - * of a class outside the current package, the receiver argument will
1.244 - * be narrowed to the type of the accessing class.
1.245 - * <p>
1.246 - * When a method handle to a virtual method is invoked, the method is
1.247 - * always looked up in the receiver (that is, the first argument).
1.248 - * <p>
1.249 - * A non-virtual method handle to a specific virtual method implementation
1.250 - * can also be created. These do not perform virtual lookup based on
1.251 - * receiver type. Such a method handle simulates the effect of
1.252 - * an {@code invokespecial} instruction to the same method.
1.253 - *
1.254 - * <h1>Usage examples</h1>
1.255 - * Here are some examples of usage:
1.256 - * <blockquote><pre>{@code
1.257 -Object x, y; String s; int i;
1.258 -MethodType mt; MethodHandle mh;
1.259 -MethodHandles.Lookup lookup = MethodHandles.lookup();
1.260 -// mt is (char,char)String
1.261 -mt = MethodType.methodType(String.class, char.class, char.class);
1.262 -mh = lookup.findVirtual(String.class, "replace", mt);
1.263 -s = (String) mh.invokeExact("daddy",'d','n');
1.264 -// invokeExact(Ljava/lang/String;CC)Ljava/lang/String;
1.265 -assertEquals(s, "nanny");
1.266 -// weakly typed invocation (using MHs.invoke)
1.267 -s = (String) mh.invokeWithArguments("sappy", 'p', 'v');
1.268 -assertEquals(s, "savvy");
1.269 -// mt is (Object[])List
1.270 -mt = MethodType.methodType(java.util.List.class, Object[].class);
1.271 -mh = lookup.findStatic(java.util.Arrays.class, "asList", mt);
1.272 -assert(mh.isVarargsCollector());
1.273 -x = mh.invoke("one", "two");
1.274 -// invoke(Ljava/lang/String;Ljava/lang/String;)Ljava/lang/Object;
1.275 -assertEquals(x, java.util.Arrays.asList("one","two"));
1.276 -// mt is (Object,Object,Object)Object
1.277 -mt = MethodType.genericMethodType(3);
1.278 -mh = mh.asType(mt);
1.279 -x = mh.invokeExact((Object)1, (Object)2, (Object)3);
1.280 -// invokeExact(Ljava/lang/Object;Ljava/lang/Object;Ljava/lang/Object;)Ljava/lang/Object;
1.281 -assertEquals(x, java.util.Arrays.asList(1,2,3));
1.282 -// mt is ()int
1.283 -mt = MethodType.methodType(int.class);
1.284 -mh = lookup.findVirtual(java.util.List.class, "size", mt);
1.285 -i = (int) mh.invokeExact(java.util.Arrays.asList(1,2,3));
1.286 -// invokeExact(Ljava/util/List;)I
1.287 -assert(i == 3);
1.288 -mt = MethodType.methodType(void.class, String.class);
1.289 -mh = lookup.findVirtual(java.io.PrintStream.class, "println", mt);
1.290 -mh.invokeExact(System.out, "Hello, world.");
1.291 -// invokeExact(Ljava/io/PrintStream;Ljava/lang/String;)V
1.292 - * }</pre></blockquote>
1.293 - * Each of the above calls to {@code invokeExact} or plain {@code invoke}
1.294 - * generates a single invokevirtual instruction with
1.295 - * the symbolic type descriptor indicated in the following comment.
1.296 - * In these examples, the helper method {@code assertEquals} is assumed to
1.297 - * be a method which calls {@link java.util.Objects#equals(Object,Object) Objects.equals}
1.298 - * on its arguments, and asserts that the result is true.
1.299 - *
1.300 - * <h1>Exceptions</h1>
1.301 - * The methods {@code invokeExact} and {@code invoke} are declared
1.302 - * to throw {@link java.lang.Throwable Throwable},
1.303 - * which is to say that there is no static restriction on what a method handle
1.304 - * can throw. Since the JVM does not distinguish between checked
1.305 - * and unchecked exceptions (other than by their class, of course),
1.306 - * there is no particular effect on bytecode shape from ascribing
1.307 - * checked exceptions to method handle invocations. But in Java source
1.308 - * code, methods which perform method handle calls must either explicitly
1.309 - * throw {@code Throwable}, or else must catch all
1.310 - * throwables locally, rethrowing only those which are legal in the context,
1.311 - * and wrapping ones which are illegal.
1.312 - *
1.313 - * <h1><a name="sigpoly"></a>Signature polymorphism</h1>
1.314 - * The unusual compilation and linkage behavior of
1.315 - * {@code invokeExact} and plain {@code invoke}
1.316 - * is referenced by the term <em>signature polymorphism</em>.
1.317 - * As defined in the Java Language Specification,
1.318 - * a signature polymorphic method is one which can operate with
1.319 - * any of a wide range of call signatures and return types.
1.320 - * <p>
1.321 - * In source code, a call to a signature polymorphic method will
1.322 - * compile, regardless of the requested symbolic type descriptor.
1.323 - * As usual, the Java compiler emits an {@code invokevirtual}
1.324 - * instruction with the given symbolic type descriptor against the named method.
1.325 - * The unusual part is that the symbolic type descriptor is derived from
1.326 - * the actual argument and return types, not from the method declaration.
1.327 - * <p>
1.328 - * When the JVM processes bytecode containing signature polymorphic calls,
1.329 - * it will successfully link any such call, regardless of its symbolic type descriptor.
1.330 - * (In order to retain type safety, the JVM will guard such calls with suitable
1.331 - * dynamic type checks, as described elsewhere.)
1.332 - * <p>
1.333 - * Bytecode generators, including the compiler back end, are required to emit
1.334 - * untransformed symbolic type descriptors for these methods.
1.335 - * Tools which determine symbolic linkage are required to accept such
1.336 - * untransformed descriptors, without reporting linkage errors.
1.337 - *
1.338 - * <h1>Interoperation between method handles and the Core Reflection API</h1>
1.339 - * Using factory methods in the {@link java.lang.invoke.MethodHandles.Lookup Lookup} API,
1.340 - * any class member represented by a Core Reflection API object
1.341 - * can be converted to a behaviorally equivalent method handle.
1.342 - * For example, a reflective {@link java.lang.reflect.Method Method} can
1.343 - * be converted to a method handle using
1.344 - * {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect}.
1.345 - * The resulting method handles generally provide more direct and efficient
1.346 - * access to the underlying class members.
1.347 - * <p>
1.348 - * As a special case,
1.349 - * when the Core Reflection API is used to view the signature polymorphic
1.350 - * methods {@code invokeExact} or plain {@code invoke} in this class,
1.351 - * they appear as ordinary non-polymorphic methods.
1.352 - * Their reflective appearance, as viewed by
1.353 - * {@link java.lang.Class#getDeclaredMethod Class.getDeclaredMethod},
1.354 - * is unaffected by their special status in this API.
1.355 - * For example, {@link java.lang.reflect.Method#getModifiers Method.getModifiers}
1.356 - * will report exactly those modifier bits required for any similarly
1.357 - * declared method, including in this case {@code native} and {@code varargs} bits.
1.358 - * <p>
1.359 - * As with any reflected method, these methods (when reflected) may be
1.360 - * invoked via {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}.
1.361 - * However, such reflective calls do not result in method handle invocations.
1.362 - * Such a call, if passed the required argument
1.363 - * (a single one, of type {@code Object[]}), will ignore the argument and
1.364 - * will throw an {@code UnsupportedOperationException}.
1.365 - * <p>
1.366 - * Since {@code invokevirtual} instructions can natively
1.367 - * invoke method handles under any symbolic type descriptor, this reflective view conflicts
1.368 - * with the normal presentation of these methods via bytecodes.
1.369 - * Thus, these two native methods, when reflectively viewed by
1.370 - * {@code Class.getDeclaredMethod}, may be regarded as placeholders only.
1.371 - * <p>
1.372 - * In order to obtain an invoker method for a particular type descriptor,
1.373 - * use {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker},
1.374 - * or {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}.
1.375 - * The {@link java.lang.invoke.MethodHandles.Lookup#findVirtual Lookup.findVirtual}
1.376 - * API is also able to return a method handle
1.377 - * to call {@code invokeExact} or plain {@code invoke},
1.378 - * for any specified type descriptor .
1.379 - *
1.380 - * <h1>Interoperation between method handles and Java generics</h1>
1.381 - * A method handle can be obtained on a method, constructor, or field
1.382 - * which is declared with Java generic types.
1.383 - * As with the Core Reflection API, the type of the method handle
1.384 - * will constructed from the erasure of the source-level type.
1.385 - * When a method handle is invoked, the types of its arguments
1.386 - * or the return value cast type may be generic types or type instances.
1.387 - * If this occurs, the compiler will replace those
1.388 - * types by their erasures when it constructs the symbolic type descriptor
1.389 - * for the {@code invokevirtual} instruction.
1.390 - * <p>
1.391 - * Method handles do not represent
1.392 - * their function-like types in terms of Java parameterized (generic) types,
1.393 - * because there are three mismatches between function-like types and parameterized
1.394 - * Java types.
1.395 - * <ul>
1.396 - * <li>Method types range over all possible arities,
1.397 - * from no arguments to up to the <a href="MethodHandle.html#maxarity">maximum number</a> of allowed arguments.
1.398 - * Generics are not variadic, and so cannot represent this.</li>
1.399 - * <li>Method types can specify arguments of primitive types,
1.400 - * which Java generic types cannot range over.</li>
1.401 - * <li>Higher order functions over method handles (combinators) are
1.402 - * often generic across a wide range of function types, including
1.403 - * those of multiple arities. It is impossible to represent such
1.404 - * genericity with a Java type parameter.</li>
1.405 - * </ul>
1.406 - *
1.407 - * <h1><a name="maxarity"></a>Arity limits</h1>
1.408 - * The JVM imposes on all methods and constructors of any kind an absolute
1.409 - * limit of 255 stacked arguments. This limit can appear more restrictive
1.410 - * in certain cases:
1.411 - * <ul>
1.412 - * <li>A {@code long} or {@code double} argument counts (for purposes of arity limits) as two argument slots.
1.413 - * <li>A non-static method consumes an extra argument for the object on which the method is called.
1.414 - * <li>A constructor consumes an extra argument for the object which is being constructed.
1.415 - * <li>Since a method handle’s {@code invoke} method (or other signature-polymorphic method) is non-virtual,
1.416 - * it consumes an extra argument for the method handle itself, in addition to any non-virtual receiver object.
1.417 - * </ul>
1.418 - * These limits imply that certain method handles cannot be created, solely because of the JVM limit on stacked arguments.
1.419 - * For example, if a static JVM method accepts exactly 255 arguments, a method handle cannot be created for it.
1.420 - * Attempts to create method handles with impossible method types lead to an {@link IllegalArgumentException}.
1.421 - * In particular, a method handle’s type must not have an arity of the exact maximum 255.
1.422 - *
1.423 - * @see MethodType
1.424 - * @see MethodHandles
1.425 - * @author John Rose, JSR 292 EG
1.426 - */
1.427 -public abstract class MethodHandle {
1.428 - static { MethodHandleImpl.initStatics(); }
1.429 -
1.430 - /**
1.431 - * Internal marker interface which distinguishes (to the Java compiler)
1.432 - * those methods which are <a href="MethodHandle.html#sigpoly">signature polymorphic</a>.
1.433 - */
1.434 - @java.lang.annotation.Target({java.lang.annotation.ElementType.METHOD})
1.435 - @java.lang.annotation.Retention(java.lang.annotation.RetentionPolicy.RUNTIME)
1.436 - @interface PolymorphicSignature { }
1.437 -
1.438 - private final MethodType type;
1.439 - /*private*/ LambdaForm form;
1.440 - // form is not private so that invokers can easily fetch it
1.441 - /*private*/ MethodHandle asTypeCache;
1.442 - // asTypeCache is not private so that invokers can easily fetch it
1.443 -
1.444 - /**
1.445 - * Reports the type of this method handle.
1.446 - * Every invocation of this method handle via {@code invokeExact} must exactly match this type.
1.447 - * @return the method handle type
1.448 - */
1.449 - public MethodType type() {
1.450 - return type;
1.451 - }
1.452 -
1.453 - /**
1.454 - * Package-private constructor for the method handle implementation hierarchy.
1.455 - * Method handle inheritance will be contained completely within
1.456 - * the {@code java.lang.invoke} package.
1.457 - */
1.458 - // @param type type (permanently assigned) of the new method handle
1.459 - /*non-public*/ MethodHandle(MethodType type, LambdaForm form) {
1.460 - type.getClass(); // explicit NPE
1.461 - form.getClass(); // explicit NPE
1.462 - this.type = type;
1.463 - this.form = form;
1.464 -
1.465 - form.prepare(); // TO DO: Try to delay this step until just before invocation.
1.466 - }
1.467 -
1.468 - /**
1.469 - * Invokes the method handle, allowing any caller type descriptor, but requiring an exact type match.
1.470 - * The symbolic type descriptor at the call site of {@code invokeExact} must
1.471 - * exactly match this method handle's {@link #type type}.
1.472 - * No conversions are allowed on arguments or return values.
1.473 - * <p>
1.474 - * When this method is observed via the Core Reflection API,
1.475 - * it will appear as a single native method, taking an object array and returning an object.
1.476 - * If this native method is invoked directly via
1.477 - * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}, via JNI,
1.478 - * or indirectly via {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect},
1.479 - * it will throw an {@code UnsupportedOperationException}.
1.480 - * @param args the signature-polymorphic parameter list, statically represented using varargs
1.481 - * @return the signature-polymorphic result, statically represented using {@code Object}
1.482 - * @throws WrongMethodTypeException if the target's type is not identical with the caller's symbolic type descriptor
1.483 - * @throws Throwable anything thrown by the underlying method propagates unchanged through the method handle call
1.484 - */
1.485 - public final native @PolymorphicSignature Object invokeExact(Object... args) throws Throwable;
1.486 -
1.487 - /**
1.488 - * Invokes the method handle, allowing any caller type descriptor,
1.489 - * and optionally performing conversions on arguments and return values.
1.490 - * <p>
1.491 - * If the call site's symbolic type descriptor exactly matches this method handle's {@link #type type},
1.492 - * the call proceeds as if by {@link #invokeExact invokeExact}.
1.493 - * <p>
1.494 - * Otherwise, the call proceeds as if this method handle were first
1.495 - * adjusted by calling {@link #asType asType} to adjust this method handle
1.496 - * to the required type, and then the call proceeds as if by
1.497 - * {@link #invokeExact invokeExact} on the adjusted method handle.
1.498 - * <p>
1.499 - * There is no guarantee that the {@code asType} call is actually made.
1.500 - * If the JVM can predict the results of making the call, it may perform
1.501 - * adaptations directly on the caller's arguments,
1.502 - * and call the target method handle according to its own exact type.
1.503 - * <p>
1.504 - * The resolved type descriptor at the call site of {@code invoke} must
1.505 - * be a valid argument to the receivers {@code asType} method.
1.506 - * In particular, the caller must specify the same argument arity
1.507 - * as the callee's type,
1.508 - * if the callee is not a {@linkplain #asVarargsCollector variable arity collector}.
1.509 - * <p>
1.510 - * When this method is observed via the Core Reflection API,
1.511 - * it will appear as a single native method, taking an object array and returning an object.
1.512 - * If this native method is invoked directly via
1.513 - * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}, via JNI,
1.514 - * or indirectly via {@link java.lang.invoke.MethodHandles.Lookup#unreflect Lookup.unreflect},
1.515 - * it will throw an {@code UnsupportedOperationException}.
1.516 - * @param args the signature-polymorphic parameter list, statically represented using varargs
1.517 - * @return the signature-polymorphic result, statically represented using {@code Object}
1.518 - * @throws WrongMethodTypeException if the target's type cannot be adjusted to the caller's symbolic type descriptor
1.519 - * @throws ClassCastException if the target's type can be adjusted to the caller, but a reference cast fails
1.520 - * @throws Throwable anything thrown by the underlying method propagates unchanged through the method handle call
1.521 - */
1.522 - public final native @PolymorphicSignature Object invoke(Object... args) throws Throwable;
1.523 -
1.524 - /**
1.525 - * Private method for trusted invocation of a method handle respecting simplified signatures.
1.526 - * Type mismatches will not throw {@code WrongMethodTypeException}, but could crash the JVM.
1.527 - * <p>
1.528 - * The caller signature is restricted to the following basic types:
1.529 - * Object, int, long, float, double, and void return.
1.530 - * <p>
1.531 - * The caller is responsible for maintaining type correctness by ensuring
1.532 - * that the each outgoing argument value is a member of the range of the corresponding
1.533 - * callee argument type.
1.534 - * (The caller should therefore issue appropriate casts and integer narrowing
1.535 - * operations on outgoing argument values.)
1.536 - * The caller can assume that the incoming result value is part of the range
1.537 - * of the callee's return type.
1.538 - * @param args the signature-polymorphic parameter list, statically represented using varargs
1.539 - * @return the signature-polymorphic result, statically represented using {@code Object}
1.540 - */
1.541 - /*non-public*/ final native @PolymorphicSignature Object invokeBasic(Object... args) throws Throwable;
1.542 -
1.543 - /**
1.544 - * Private method for trusted invocation of a MemberName of kind {@code REF_invokeVirtual}.
1.545 - * The caller signature is restricted to basic types as with {@code invokeBasic}.
1.546 - * The trailing (not leading) argument must be a MemberName.
1.547 - * @param args the signature-polymorphic parameter list, statically represented using varargs
1.548 - * @return the signature-polymorphic result, statically represented using {@code Object}
1.549 - */
1.550 - /*non-public*/ static native @PolymorphicSignature Object linkToVirtual(Object... args) throws Throwable;
1.551 -
1.552 - /**
1.553 - * Private method for trusted invocation of a MemberName of kind {@code REF_invokeStatic}.
1.554 - * The caller signature is restricted to basic types as with {@code invokeBasic}.
1.555 - * The trailing (not leading) argument must be a MemberName.
1.556 - * @param args the signature-polymorphic parameter list, statically represented using varargs
1.557 - * @return the signature-polymorphic result, statically represented using {@code Object}
1.558 - */
1.559 - /*non-public*/ static native @PolymorphicSignature Object linkToStatic(Object... args) throws Throwable;
1.560 -
1.561 - /**
1.562 - * Private method for trusted invocation of a MemberName of kind {@code REF_invokeSpecial}.
1.563 - * The caller signature is restricted to basic types as with {@code invokeBasic}.
1.564 - * The trailing (not leading) argument must be a MemberName.
1.565 - * @param args the signature-polymorphic parameter list, statically represented using varargs
1.566 - * @return the signature-polymorphic result, statically represented using {@code Object}
1.567 - */
1.568 - /*non-public*/ static native @PolymorphicSignature Object linkToSpecial(Object... args) throws Throwable;
1.569 -
1.570 - /**
1.571 - * Private method for trusted invocation of a MemberName of kind {@code REF_invokeInterface}.
1.572 - * The caller signature is restricted to basic types as with {@code invokeBasic}.
1.573 - * The trailing (not leading) argument must be a MemberName.
1.574 - * @param args the signature-polymorphic parameter list, statically represented using varargs
1.575 - * @return the signature-polymorphic result, statically represented using {@code Object}
1.576 - */
1.577 - /*non-public*/ static native @PolymorphicSignature Object linkToInterface(Object... args) throws Throwable;
1.578 -
1.579 - /**
1.580 - * Performs a variable arity invocation, passing the arguments in the given list
1.581 - * to the method handle, as if via an inexact {@link #invoke invoke} from a call site
1.582 - * which mentions only the type {@code Object}, and whose arity is the length
1.583 - * of the argument list.
1.584 - * <p>
1.585 - * Specifically, execution proceeds as if by the following steps,
1.586 - * although the methods are not guaranteed to be called if the JVM
1.587 - * can predict their effects.
1.588 - * <ul>
1.589 - * <li>Determine the length of the argument array as {@code N}.
1.590 - * For a null reference, {@code N=0}. </li>
1.591 - * <li>Determine the general type {@code TN} of {@code N} arguments as
1.592 - * as {@code TN=MethodType.genericMethodType(N)}.</li>
1.593 - * <li>Force the original target method handle {@code MH0} to the
1.594 - * required type, as {@code MH1 = MH0.asType(TN)}. </li>
1.595 - * <li>Spread the array into {@code N} separate arguments {@code A0, ...}. </li>
1.596 - * <li>Invoke the type-adjusted method handle on the unpacked arguments:
1.597 - * MH1.invokeExact(A0, ...). </li>
1.598 - * <li>Take the return value as an {@code Object} reference. </li>
1.599 - * </ul>
1.600 - * <p>
1.601 - * Because of the action of the {@code asType} step, the following argument
1.602 - * conversions are applied as necessary:
1.603 - * <ul>
1.604 - * <li>reference casting
1.605 - * <li>unboxing
1.606 - * <li>widening primitive conversions
1.607 - * </ul>
1.608 - * <p>
1.609 - * The result returned by the call is boxed if it is a primitive,
1.610 - * or forced to null if the return type is void.
1.611 - * <p>
1.612 - * This call is equivalent to the following code:
1.613 - * <blockquote><pre>{@code
1.614 - * MethodHandle invoker = MethodHandles.spreadInvoker(this.type(), 0);
1.615 - * Object result = invoker.invokeExact(this, arguments);
1.616 - * }</pre></blockquote>
1.617 - * <p>
1.618 - * Unlike the signature polymorphic methods {@code invokeExact} and {@code invoke},
1.619 - * {@code invokeWithArguments} can be accessed normally via the Core Reflection API and JNI.
1.620 - * It can therefore be used as a bridge between native or reflective code and method handles.
1.621 - *
1.622 - * @param arguments the arguments to pass to the target
1.623 - * @return the result returned by the target
1.624 - * @throws ClassCastException if an argument cannot be converted by reference casting
1.625 - * @throws WrongMethodTypeException if the target's type cannot be adjusted to take the given number of {@code Object} arguments
1.626 - * @throws Throwable anything thrown by the target method invocation
1.627 - * @see MethodHandles#spreadInvoker
1.628 - */
1.629 - public Object invokeWithArguments(Object... arguments) throws Throwable {
1.630 - int argc = arguments == null ? 0 : arguments.length;
1.631 - @SuppressWarnings("LocalVariableHidesMemberVariable")
1.632 - MethodType type = type();
1.633 - if (type.parameterCount() != argc || isVarargsCollector()) {
1.634 - // simulate invoke
1.635 - return asType(MethodType.genericMethodType(argc)).invokeWithArguments(arguments);
1.636 - }
1.637 - MethodHandle invoker = type.invokers().varargsInvoker();
1.638 - return invoker.invokeExact(this, arguments);
1.639 - }
1.640 -
1.641 - /**
1.642 - * Performs a variable arity invocation, passing the arguments in the given array
1.643 - * to the method handle, as if via an inexact {@link #invoke invoke} from a call site
1.644 - * which mentions only the type {@code Object}, and whose arity is the length
1.645 - * of the argument array.
1.646 - * <p>
1.647 - * This method is also equivalent to the following code:
1.648 - * <blockquote><pre>{@code
1.649 - * invokeWithArguments(arguments.toArray()
1.650 - * }</pre></blockquote>
1.651 - *
1.652 - * @param arguments the arguments to pass to the target
1.653 - * @return the result returned by the target
1.654 - * @throws NullPointerException if {@code arguments} is a null reference
1.655 - * @throws ClassCastException if an argument cannot be converted by reference casting
1.656 - * @throws WrongMethodTypeException if the target's type cannot be adjusted to take the given number of {@code Object} arguments
1.657 - * @throws Throwable anything thrown by the target method invocation
1.658 - */
1.659 - public Object invokeWithArguments(java.util.List<?> arguments) throws Throwable {
1.660 - return invokeWithArguments(arguments.toArray());
1.661 - }
1.662 -
1.663 - /**
1.664 - * Produces an adapter method handle which adapts the type of the
1.665 - * current method handle to a new type.
1.666 - * The resulting method handle is guaranteed to report a type
1.667 - * which is equal to the desired new type.
1.668 - * <p>
1.669 - * If the original type and new type are equal, returns {@code this}.
1.670 - * <p>
1.671 - * The new method handle, when invoked, will perform the following
1.672 - * steps:
1.673 - * <ul>
1.674 - * <li>Convert the incoming argument list to match the original
1.675 - * method handle's argument list.
1.676 - * <li>Invoke the original method handle on the converted argument list.
1.677 - * <li>Convert any result returned by the original method handle
1.678 - * to the return type of new method handle.
1.679 - * </ul>
1.680 - * <p>
1.681 - * This method provides the crucial behavioral difference between
1.682 - * {@link #invokeExact invokeExact} and plain, inexact {@link #invoke invoke}.
1.683 - * The two methods
1.684 - * perform the same steps when the caller's type descriptor exactly m atches
1.685 - * the callee's, but when the types differ, plain {@link #invoke invoke}
1.686 - * also calls {@code asType} (or some internal equivalent) in order
1.687 - * to match up the caller's and callee's types.
1.688 - * <p>
1.689 - * If the current method is a variable arity method handle
1.690 - * argument list conversion may involve the conversion and collection
1.691 - * of several arguments into an array, as
1.692 - * {@linkplain #asVarargsCollector described elsewhere}.
1.693 - * In every other case, all conversions are applied <em>pairwise</em>,
1.694 - * which means that each argument or return value is converted to
1.695 - * exactly one argument or return value (or no return value).
1.696 - * The applied conversions are defined by consulting the
1.697 - * the corresponding component types of the old and new
1.698 - * method handle types.
1.699 - * <p>
1.700 - * Let <em>T0</em> and <em>T1</em> be corresponding new and old parameter types,
1.701 - * or old and new return types. Specifically, for some valid index {@code i}, let
1.702 - * <em>T0</em>{@code =newType.parameterType(i)} and <em>T1</em>{@code =this.type().parameterType(i)}.
1.703 - * Or else, going the other way for return values, let
1.704 - * <em>T0</em>{@code =this.type().returnType()} and <em>T1</em>{@code =newType.returnType()}.
1.705 - * If the types are the same, the new method handle makes no change
1.706 - * to the corresponding argument or return value (if any).
1.707 - * Otherwise, one of the following conversions is applied
1.708 - * if possible:
1.709 - * <ul>
1.710 - * <li>If <em>T0</em> and <em>T1</em> are references, then a cast to <em>T1</em> is applied.
1.711 - * (The types do not need to be related in any particular way.
1.712 - * This is because a dynamic value of null can convert to any reference type.)
1.713 - * <li>If <em>T0</em> and <em>T1</em> are primitives, then a Java method invocation
1.714 - * conversion (JLS 5.3) is applied, if one exists.
1.715 - * (Specifically, <em>T0</em> must convert to <em>T1</em> by a widening primitive conversion.)
1.716 - * <li>If <em>T0</em> is a primitive and <em>T1</em> a reference,
1.717 - * a Java casting conversion (JLS 5.5) is applied if one exists.
1.718 - * (Specifically, the value is boxed from <em>T0</em> to its wrapper class,
1.719 - * which is then widened as needed to <em>T1</em>.)
1.720 - * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
1.721 - * conversion will be applied at runtime, possibly followed
1.722 - * by a Java method invocation conversion (JLS 5.3)
1.723 - * on the primitive value. (These are the primitive widening conversions.)
1.724 - * <em>T0</em> must be a wrapper class or a supertype of one.
1.725 - * (In the case where <em>T0</em> is Object, these are the conversions
1.726 - * allowed by {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}.)
1.727 - * The unboxing conversion must have a possibility of success, which means that
1.728 - * if <em>T0</em> is not itself a wrapper class, there must exist at least one
1.729 - * wrapper class <em>TW</em> which is a subtype of <em>T0</em> and whose unboxed
1.730 - * primitive value can be widened to <em>T1</em>.
1.731 - * <li>If the return type <em>T1</em> is marked as void, any returned value is discarded
1.732 - * <li>If the return type <em>T0</em> is void and <em>T1</em> a reference, a null value is introduced.
1.733 - * <li>If the return type <em>T0</em> is void and <em>T1</em> a primitive,
1.734 - * a zero value is introduced.
1.735 - * </ul>
1.736 - * (<em>Note:</em> Both <em>T0</em> and <em>T1</em> may be regarded as static types,
1.737 - * because neither corresponds specifically to the <em>dynamic type</em> of any
1.738 - * actual argument or return value.)
1.739 - * <p>
1.740 - * The method handle conversion cannot be made if any one of the required
1.741 - * pairwise conversions cannot be made.
1.742 - * <p>
1.743 - * At runtime, the conversions applied to reference arguments
1.744 - * or return values may require additional runtime checks which can fail.
1.745 - * An unboxing operation may fail because the original reference is null,
1.746 - * causing a {@link java.lang.NullPointerException NullPointerException}.
1.747 - * An unboxing operation or a reference cast may also fail on a reference
1.748 - * to an object of the wrong type,
1.749 - * causing a {@link java.lang.ClassCastException ClassCastException}.
1.750 - * Although an unboxing operation may accept several kinds of wrappers,
1.751 - * if none are available, a {@code ClassCastException} will be thrown.
1.752 - *
1.753 - * @param newType the expected type of the new method handle
1.754 - * @return a method handle which delegates to {@code this} after performing
1.755 - * any necessary argument conversions, and arranges for any
1.756 - * necessary return value conversions
1.757 - * @throws NullPointerException if {@code newType} is a null reference
1.758 - * @throws WrongMethodTypeException if the conversion cannot be made
1.759 - * @see MethodHandles#explicitCastArguments
1.760 - */
1.761 - public MethodHandle asType(MethodType newType) {
1.762 - // Fast path alternative to a heavyweight {@code asType} call.
1.763 - // Return 'this' if the conversion will be a no-op.
1.764 - if (newType == type) {
1.765 - return this;
1.766 - }
1.767 - // Return 'this.asTypeCache' if the conversion is already memoized.
1.768 - MethodHandle atc = asTypeCache;
1.769 - if (atc != null && newType == atc.type) {
1.770 - return atc;
1.771 - }
1.772 - return asTypeUncached(newType);
1.773 - }
1.774 -
1.775 - /** Override this to change asType behavior. */
1.776 - /*non-public*/ MethodHandle asTypeUncached(MethodType newType) {
1.777 - if (!type.isConvertibleTo(newType))
1.778 - throw new WrongMethodTypeException("cannot convert "+this+" to "+newType);
1.779 - return asTypeCache = convertArguments(newType);
1.780 - }
1.781 -
1.782 - /**
1.783 - * Makes an <em>array-spreading</em> method handle, which accepts a trailing array argument
1.784 - * and spreads its elements as positional arguments.
1.785 - * The new method handle adapts, as its <i>target</i>,
1.786 - * the current method handle. The type of the adapter will be
1.787 - * the same as the type of the target, except that the final
1.788 - * {@code arrayLength} parameters of the target's type are replaced
1.789 - * by a single array parameter of type {@code arrayType}.
1.790 - * <p>
1.791 - * If the array element type differs from any of the corresponding
1.792 - * argument types on the original target,
1.793 - * the original target is adapted to take the array elements directly,
1.794 - * as if by a call to {@link #asType asType}.
1.795 - * <p>
1.796 - * When called, the adapter replaces a trailing array argument
1.797 - * by the array's elements, each as its own argument to the target.
1.798 - * (The order of the arguments is preserved.)
1.799 - * They are converted pairwise by casting and/or unboxing
1.800 - * to the types of the trailing parameters of the target.
1.801 - * Finally the target is called.
1.802 - * What the target eventually returns is returned unchanged by the adapter.
1.803 - * <p>
1.804 - * Before calling the target, the adapter verifies that the array
1.805 - * contains exactly enough elements to provide a correct argument count
1.806 - * to the target method handle.
1.807 - * (The array may also be null when zero elements are required.)
1.808 - * <p>
1.809 - * If, when the adapter is called, the supplied array argument does
1.810 - * not have the correct number of elements, the adapter will throw
1.811 - * an {@link IllegalArgumentException} instead of invoking the target.
1.812 - * <p>
1.813 - * Here are some simple examples of array-spreading method handles:
1.814 - * <blockquote><pre>{@code
1.815 -MethodHandle equals = publicLookup()
1.816 - .findVirtual(String.class, "equals", methodType(boolean.class, Object.class));
1.817 -assert( (boolean) equals.invokeExact("me", (Object)"me"));
1.818 -assert(!(boolean) equals.invokeExact("me", (Object)"thee"));
1.819 -// spread both arguments from a 2-array:
1.820 -MethodHandle eq2 = equals.asSpreader(Object[].class, 2);
1.821 -assert( (boolean) eq2.invokeExact(new Object[]{ "me", "me" }));
1.822 -assert(!(boolean) eq2.invokeExact(new Object[]{ "me", "thee" }));
1.823 -// try to spread from anything but a 2-array:
1.824 -for (int n = 0; n <= 10; n++) {
1.825 - Object[] badArityArgs = (n == 2 ? null : new Object[n]);
1.826 - try { assert((boolean) eq2.invokeExact(badArityArgs) && false); }
1.827 - catch (IllegalArgumentException ex) { } // OK
1.828 -}
1.829 -// spread both arguments from a String array:
1.830 -MethodHandle eq2s = equals.asSpreader(String[].class, 2);
1.831 -assert( (boolean) eq2s.invokeExact(new String[]{ "me", "me" }));
1.832 -assert(!(boolean) eq2s.invokeExact(new String[]{ "me", "thee" }));
1.833 -// spread second arguments from a 1-array:
1.834 -MethodHandle eq1 = equals.asSpreader(Object[].class, 1);
1.835 -assert( (boolean) eq1.invokeExact("me", new Object[]{ "me" }));
1.836 -assert(!(boolean) eq1.invokeExact("me", new Object[]{ "thee" }));
1.837 -// spread no arguments from a 0-array or null:
1.838 -MethodHandle eq0 = equals.asSpreader(Object[].class, 0);
1.839 -assert( (boolean) eq0.invokeExact("me", (Object)"me", new Object[0]));
1.840 -assert(!(boolean) eq0.invokeExact("me", (Object)"thee", (Object[])null));
1.841 -// asSpreader and asCollector are approximate inverses:
1.842 -for (int n = 0; n <= 2; n++) {
1.843 - for (Class<?> a : new Class<?>[]{Object[].class, String[].class, CharSequence[].class}) {
1.844 - MethodHandle equals2 = equals.asSpreader(a, n).asCollector(a, n);
1.845 - assert( (boolean) equals2.invokeWithArguments("me", "me"));
1.846 - assert(!(boolean) equals2.invokeWithArguments("me", "thee"));
1.847 - }
1.848 -}
1.849 -MethodHandle caToString = publicLookup()
1.850 - .findStatic(Arrays.class, "toString", methodType(String.class, char[].class));
1.851 -assertEquals("[A, B, C]", (String) caToString.invokeExact("ABC".toCharArray()));
1.852 -MethodHandle caString3 = caToString.asCollector(char[].class, 3);
1.853 -assertEquals("[A, B, C]", (String) caString3.invokeExact('A', 'B', 'C'));
1.854 -MethodHandle caToString2 = caString3.asSpreader(char[].class, 2);
1.855 -assertEquals("[A, B, C]", (String) caToString2.invokeExact('A', "BC".toCharArray()));
1.856 - * }</pre></blockquote>
1.857 - * @param arrayType usually {@code Object[]}, the type of the array argument from which to extract the spread arguments
1.858 - * @param arrayLength the number of arguments to spread from an incoming array argument
1.859 - * @return a new method handle which spreads its final array argument,
1.860 - * before calling the original method handle
1.861 - * @throws NullPointerException if {@code arrayType} is a null reference
1.862 - * @throws IllegalArgumentException if {@code arrayType} is not an array type,
1.863 - * or if target does not have at least
1.864 - * {@code arrayLength} parameter types,
1.865 - * or if {@code arrayLength} is negative,
1.866 - * or if the resulting method handle's type would have
1.867 - * <a href="MethodHandle.html#maxarity">too many parameters</a>
1.868 - * @throws WrongMethodTypeException if the implied {@code asType} call fails
1.869 - * @see #asCollector
1.870 - */
1.871 - public MethodHandle asSpreader(Class<?> arrayType, int arrayLength) {
1.872 - asSpreaderChecks(arrayType, arrayLength);
1.873 - int spreadArgPos = type.parameterCount() - arrayLength;
1.874 - return MethodHandleImpl.makeSpreadArguments(this, arrayType, spreadArgPos, arrayLength);
1.875 - }
1.876 -
1.877 - private void asSpreaderChecks(Class<?> arrayType, int arrayLength) {
1.878 - spreadArrayChecks(arrayType, arrayLength);
1.879 - int nargs = type().parameterCount();
1.880 - if (nargs < arrayLength || arrayLength < 0)
1.881 - throw newIllegalArgumentException("bad spread array length");
1.882 - if (arrayType != Object[].class && arrayLength != 0) {
1.883 - boolean sawProblem = false;
1.884 - Class<?> arrayElement = arrayType.getComponentType();
1.885 - for (int i = nargs - arrayLength; i < nargs; i++) {
1.886 - if (!MethodType.canConvert(arrayElement, type().parameterType(i))) {
1.887 - sawProblem = true;
1.888 - break;
1.889 - }
1.890 - }
1.891 - if (sawProblem) {
1.892 - ArrayList<Class<?>> ptypes = new ArrayList<>(type().parameterList());
1.893 - for (int i = nargs - arrayLength; i < nargs; i++) {
1.894 - ptypes.set(i, arrayElement);
1.895 - }
1.896 - // elicit an error:
1.897 - this.asType(MethodType.methodType(type().returnType(), ptypes));
1.898 - }
1.899 - }
1.900 - }
1.901 -
1.902 - private void spreadArrayChecks(Class<?> arrayType, int arrayLength) {
1.903 - Class<?> arrayElement = arrayType.getComponentType();
1.904 - if (arrayElement == null)
1.905 - throw newIllegalArgumentException("not an array type", arrayType);
1.906 - if ((arrayLength & 0x7F) != arrayLength) {
1.907 - if ((arrayLength & 0xFF) != arrayLength)
1.908 - throw newIllegalArgumentException("array length is not legal", arrayLength);
1.909 - assert(arrayLength >= 128);
1.910 - if (arrayElement == long.class ||
1.911 - arrayElement == double.class)
1.912 - throw newIllegalArgumentException("array length is not legal for long[] or double[]", arrayLength);
1.913 - }
1.914 - }
1.915 -
1.916 - /**
1.917 - * Makes an <em>array-collecting</em> method handle, which accepts a given number of trailing
1.918 - * positional arguments and collects them into an array argument.
1.919 - * The new method handle adapts, as its <i>target</i>,
1.920 - * the current method handle. The type of the adapter will be
1.921 - * the same as the type of the target, except that a single trailing
1.922 - * parameter (usually of type {@code arrayType}) is replaced by
1.923 - * {@code arrayLength} parameters whose type is element type of {@code arrayType}.
1.924 - * <p>
1.925 - * If the array type differs from the final argument type on the original target,
1.926 - * the original target is adapted to take the array type directly,
1.927 - * as if by a call to {@link #asType asType}.
1.928 - * <p>
1.929 - * When called, the adapter replaces its trailing {@code arrayLength}
1.930 - * arguments by a single new array of type {@code arrayType}, whose elements
1.931 - * comprise (in order) the replaced arguments.
1.932 - * Finally the target is called.
1.933 - * What the target eventually returns is returned unchanged by the adapter.
1.934 - * <p>
1.935 - * (The array may also be a shared constant when {@code arrayLength} is zero.)
1.936 - * <p>
1.937 - * (<em>Note:</em> The {@code arrayType} is often identical to the last
1.938 - * parameter type of the original target.
1.939 - * It is an explicit argument for symmetry with {@code asSpreader}, and also
1.940 - * to allow the target to use a simple {@code Object} as its last parameter type.)
1.941 - * <p>
1.942 - * In order to create a collecting adapter which is not restricted to a particular
1.943 - * number of collected arguments, use {@link #asVarargsCollector asVarargsCollector} instead.
1.944 - * <p>
1.945 - * Here are some examples of array-collecting method handles:
1.946 - * <blockquote><pre>{@code
1.947 -MethodHandle deepToString = publicLookup()
1.948 - .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
1.949 -assertEquals("[won]", (String) deepToString.invokeExact(new Object[]{"won"}));
1.950 -MethodHandle ts1 = deepToString.asCollector(Object[].class, 1);
1.951 -assertEquals(methodType(String.class, Object.class), ts1.type());
1.952 -//assertEquals("[won]", (String) ts1.invokeExact( new Object[]{"won"})); //FAIL
1.953 -assertEquals("[[won]]", (String) ts1.invokeExact((Object) new Object[]{"won"}));
1.954 -// arrayType can be a subtype of Object[]
1.955 -MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
1.956 -assertEquals(methodType(String.class, String.class, String.class), ts2.type());
1.957 -assertEquals("[two, too]", (String) ts2.invokeExact("two", "too"));
1.958 -MethodHandle ts0 = deepToString.asCollector(Object[].class, 0);
1.959 -assertEquals("[]", (String) ts0.invokeExact());
1.960 -// collectors can be nested, Lisp-style
1.961 -MethodHandle ts22 = deepToString.asCollector(Object[].class, 3).asCollector(String[].class, 2);
1.962 -assertEquals("[A, B, [C, D]]", ((String) ts22.invokeExact((Object)'A', (Object)"B", "C", "D")));
1.963 -// arrayType can be any primitive array type
1.964 -MethodHandle bytesToString = publicLookup()
1.965 - .findStatic(Arrays.class, "toString", methodType(String.class, byte[].class))
1.966 - .asCollector(byte[].class, 3);
1.967 -assertEquals("[1, 2, 3]", (String) bytesToString.invokeExact((byte)1, (byte)2, (byte)3));
1.968 -MethodHandle longsToString = publicLookup()
1.969 - .findStatic(Arrays.class, "toString", methodType(String.class, long[].class))
1.970 - .asCollector(long[].class, 1);
1.971 -assertEquals("[123]", (String) longsToString.invokeExact((long)123));
1.972 - * }</pre></blockquote>
1.973 - * @param arrayType often {@code Object[]}, the type of the array argument which will collect the arguments
1.974 - * @param arrayLength the number of arguments to collect into a new array argument
1.975 - * @return a new method handle which collects some trailing argument
1.976 - * into an array, before calling the original method handle
1.977 - * @throws NullPointerException if {@code arrayType} is a null reference
1.978 - * @throws IllegalArgumentException if {@code arrayType} is not an array type
1.979 - * or {@code arrayType} is not assignable to this method handle's trailing parameter type,
1.980 - * or {@code arrayLength} is not a legal array size,
1.981 - * or the resulting method handle's type would have
1.982 - * <a href="MethodHandle.html#maxarity">too many parameters</a>
1.983 - * @throws WrongMethodTypeException if the implied {@code asType} call fails
1.984 - * @see #asSpreader
1.985 - * @see #asVarargsCollector
1.986 - */
1.987 - public MethodHandle asCollector(Class<?> arrayType, int arrayLength) {
1.988 - asCollectorChecks(arrayType, arrayLength);
1.989 - int collectArgPos = type().parameterCount()-1;
1.990 - MethodHandle target = this;
1.991 - if (arrayType != type().parameterType(collectArgPos))
1.992 - target = convertArguments(type().changeParameterType(collectArgPos, arrayType));
1.993 - MethodHandle collector = ValueConversions.varargsArray(arrayType, arrayLength);
1.994 - return MethodHandles.collectArguments(target, collectArgPos, collector);
1.995 - }
1.996 -
1.997 - // private API: return true if last param exactly matches arrayType
1.998 - private boolean asCollectorChecks(Class<?> arrayType, int arrayLength) {
1.999 - spreadArrayChecks(arrayType, arrayLength);
1.1000 - int nargs = type().parameterCount();
1.1001 - if (nargs != 0) {
1.1002 - Class<?> lastParam = type().parameterType(nargs-1);
1.1003 - if (lastParam == arrayType) return true;
1.1004 - if (lastParam.isAssignableFrom(arrayType)) return false;
1.1005 - }
1.1006 - throw newIllegalArgumentException("array type not assignable to trailing argument", this, arrayType);
1.1007 - }
1.1008 -
1.1009 - /**
1.1010 - * Makes a <em>variable arity</em> adapter which is able to accept
1.1011 - * any number of trailing positional arguments and collect them
1.1012 - * into an array argument.
1.1013 - * <p>
1.1014 - * The type and behavior of the adapter will be the same as
1.1015 - * the type and behavior of the target, except that certain
1.1016 - * {@code invoke} and {@code asType} requests can lead to
1.1017 - * trailing positional arguments being collected into target's
1.1018 - * trailing parameter.
1.1019 - * Also, the last parameter type of the adapter will be
1.1020 - * {@code arrayType}, even if the target has a different
1.1021 - * last parameter type.
1.1022 - * <p>
1.1023 - * This transformation may return {@code this} if the method handle is
1.1024 - * already of variable arity and its trailing parameter type
1.1025 - * is identical to {@code arrayType}.
1.1026 - * <p>
1.1027 - * When called with {@link #invokeExact invokeExact}, the adapter invokes
1.1028 - * the target with no argument changes.
1.1029 - * (<em>Note:</em> This behavior is different from a
1.1030 - * {@linkplain #asCollector fixed arity collector},
1.1031 - * since it accepts a whole array of indeterminate length,
1.1032 - * rather than a fixed number of arguments.)
1.1033 - * <p>
1.1034 - * When called with plain, inexact {@link #invoke invoke}, if the caller
1.1035 - * type is the same as the adapter, the adapter invokes the target as with
1.1036 - * {@code invokeExact}.
1.1037 - * (This is the normal behavior for {@code invoke} when types match.)
1.1038 - * <p>
1.1039 - * Otherwise, if the caller and adapter arity are the same, and the
1.1040 - * trailing parameter type of the caller is a reference type identical to
1.1041 - * or assignable to the trailing parameter type of the adapter,
1.1042 - * the arguments and return values are converted pairwise,
1.1043 - * as if by {@link #asType asType} on a fixed arity
1.1044 - * method handle.
1.1045 - * <p>
1.1046 - * Otherwise, the arities differ, or the adapter's trailing parameter
1.1047 - * type is not assignable from the corresponding caller type.
1.1048 - * In this case, the adapter replaces all trailing arguments from
1.1049 - * the original trailing argument position onward, by
1.1050 - * a new array of type {@code arrayType}, whose elements
1.1051 - * comprise (in order) the replaced arguments.
1.1052 - * <p>
1.1053 - * The caller type must provides as least enough arguments,
1.1054 - * and of the correct type, to satisfy the target's requirement for
1.1055 - * positional arguments before the trailing array argument.
1.1056 - * Thus, the caller must supply, at a minimum, {@code N-1} arguments,
1.1057 - * where {@code N} is the arity of the target.
1.1058 - * Also, there must exist conversions from the incoming arguments
1.1059 - * to the target's arguments.
1.1060 - * As with other uses of plain {@code invoke}, if these basic
1.1061 - * requirements are not fulfilled, a {@code WrongMethodTypeException}
1.1062 - * may be thrown.
1.1063 - * <p>
1.1064 - * In all cases, what the target eventually returns is returned unchanged by the adapter.
1.1065 - * <p>
1.1066 - * In the final case, it is exactly as if the target method handle were
1.1067 - * temporarily adapted with a {@linkplain #asCollector fixed arity collector}
1.1068 - * to the arity required by the caller type.
1.1069 - * (As with {@code asCollector}, if the array length is zero,
1.1070 - * a shared constant may be used instead of a new array.
1.1071 - * If the implied call to {@code asCollector} would throw
1.1072 - * an {@code IllegalArgumentException} or {@code WrongMethodTypeException},
1.1073 - * the call to the variable arity adapter must throw
1.1074 - * {@code WrongMethodTypeException}.)
1.1075 - * <p>
1.1076 - * The behavior of {@link #asType asType} is also specialized for
1.1077 - * variable arity adapters, to maintain the invariant that
1.1078 - * plain, inexact {@code invoke} is always equivalent to an {@code asType}
1.1079 - * call to adjust the target type, followed by {@code invokeExact}.
1.1080 - * Therefore, a variable arity adapter responds
1.1081 - * to an {@code asType} request by building a fixed arity collector,
1.1082 - * if and only if the adapter and requested type differ either
1.1083 - * in arity or trailing argument type.
1.1084 - * The resulting fixed arity collector has its type further adjusted
1.1085 - * (if necessary) to the requested type by pairwise conversion,
1.1086 - * as if by another application of {@code asType}.
1.1087 - * <p>
1.1088 - * When a method handle is obtained by executing an {@code ldc} instruction
1.1089 - * of a {@code CONSTANT_MethodHandle} constant, and the target method is marked
1.1090 - * as a variable arity method (with the modifier bit {@code 0x0080}),
1.1091 - * the method handle will accept multiple arities, as if the method handle
1.1092 - * constant were created by means of a call to {@code asVarargsCollector}.
1.1093 - * <p>
1.1094 - * In order to create a collecting adapter which collects a predetermined
1.1095 - * number of arguments, and whose type reflects this predetermined number,
1.1096 - * use {@link #asCollector asCollector} instead.
1.1097 - * <p>
1.1098 - * No method handle transformations produce new method handles with
1.1099 - * variable arity, unless they are documented as doing so.
1.1100 - * Therefore, besides {@code asVarargsCollector},
1.1101 - * all methods in {@code MethodHandle} and {@code MethodHandles}
1.1102 - * will return a method handle with fixed arity,
1.1103 - * except in the cases where they are specified to return their original
1.1104 - * operand (e.g., {@code asType} of the method handle's own type).
1.1105 - * <p>
1.1106 - * Calling {@code asVarargsCollector} on a method handle which is already
1.1107 - * of variable arity will produce a method handle with the same type and behavior.
1.1108 - * It may (or may not) return the original variable arity method handle.
1.1109 - * <p>
1.1110 - * Here is an example, of a list-making variable arity method handle:
1.1111 - * <blockquote><pre>{@code
1.1112 -MethodHandle deepToString = publicLookup()
1.1113 - .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
1.1114 -MethodHandle ts1 = deepToString.asVarargsCollector(Object[].class);
1.1115 -assertEquals("[won]", (String) ts1.invokeExact( new Object[]{"won"}));
1.1116 -assertEquals("[won]", (String) ts1.invoke( new Object[]{"won"}));
1.1117 -assertEquals("[won]", (String) ts1.invoke( "won" ));
1.1118 -assertEquals("[[won]]", (String) ts1.invoke((Object) new Object[]{"won"}));
1.1119 -// findStatic of Arrays.asList(...) produces a variable arity method handle:
1.1120 -MethodHandle asList = publicLookup()
1.1121 - .findStatic(Arrays.class, "asList", methodType(List.class, Object[].class));
1.1122 -assertEquals(methodType(List.class, Object[].class), asList.type());
1.1123 -assert(asList.isVarargsCollector());
1.1124 -assertEquals("[]", asList.invoke().toString());
1.1125 -assertEquals("[1]", asList.invoke(1).toString());
1.1126 -assertEquals("[two, too]", asList.invoke("two", "too").toString());
1.1127 -String[] argv = { "three", "thee", "tee" };
1.1128 -assertEquals("[three, thee, tee]", asList.invoke(argv).toString());
1.1129 -assertEquals("[three, thee, tee]", asList.invoke((Object[])argv).toString());
1.1130 -List ls = (List) asList.invoke((Object)argv);
1.1131 -assertEquals(1, ls.size());
1.1132 -assertEquals("[three, thee, tee]", Arrays.toString((Object[])ls.get(0)));
1.1133 - * }</pre></blockquote>
1.1134 - * <p style="font-size:smaller;">
1.1135 - * <em>Discussion:</em>
1.1136 - * These rules are designed as a dynamically-typed variation
1.1137 - * of the Java rules for variable arity methods.
1.1138 - * In both cases, callers to a variable arity method or method handle
1.1139 - * can either pass zero or more positional arguments, or else pass
1.1140 - * pre-collected arrays of any length. Users should be aware of the
1.1141 - * special role of the final argument, and of the effect of a
1.1142 - * type match on that final argument, which determines whether
1.1143 - * or not a single trailing argument is interpreted as a whole
1.1144 - * array or a single element of an array to be collected.
1.1145 - * Note that the dynamic type of the trailing argument has no
1.1146 - * effect on this decision, only a comparison between the symbolic
1.1147 - * type descriptor of the call site and the type descriptor of the method handle.)
1.1148 - *
1.1149 - * @param arrayType often {@code Object[]}, the type of the array argument which will collect the arguments
1.1150 - * @return a new method handle which can collect any number of trailing arguments
1.1151 - * into an array, before calling the original method handle
1.1152 - * @throws NullPointerException if {@code arrayType} is a null reference
1.1153 - * @throws IllegalArgumentException if {@code arrayType} is not an array type
1.1154 - * or {@code arrayType} is not assignable to this method handle's trailing parameter type
1.1155 - * @see #asCollector
1.1156 - * @see #isVarargsCollector
1.1157 - * @see #asFixedArity
1.1158 - */
1.1159 - public MethodHandle asVarargsCollector(Class<?> arrayType) {
1.1160 - Class<?> arrayElement = arrayType.getComponentType();
1.1161 - boolean lastMatch = asCollectorChecks(arrayType, 0);
1.1162 - if (isVarargsCollector() && lastMatch)
1.1163 - return this;
1.1164 - return MethodHandleImpl.makeVarargsCollector(this, arrayType);
1.1165 - }
1.1166 -
1.1167 - /**
1.1168 - * Determines if this method handle
1.1169 - * supports {@linkplain #asVarargsCollector variable arity} calls.
1.1170 - * Such method handles arise from the following sources:
1.1171 - * <ul>
1.1172 - * <li>a call to {@linkplain #asVarargsCollector asVarargsCollector}
1.1173 - * <li>a call to a {@linkplain java.lang.invoke.MethodHandles.Lookup lookup method}
1.1174 - * which resolves to a variable arity Java method or constructor
1.1175 - * <li>an {@code ldc} instruction of a {@code CONSTANT_MethodHandle}
1.1176 - * which resolves to a variable arity Java method or constructor
1.1177 - * </ul>
1.1178 - * @return true if this method handle accepts more than one arity of plain, inexact {@code invoke} calls
1.1179 - * @see #asVarargsCollector
1.1180 - * @see #asFixedArity
1.1181 - */
1.1182 - public boolean isVarargsCollector() {
1.1183 - return false;
1.1184 - }
1.1185 -
1.1186 - /**
1.1187 - * Makes a <em>fixed arity</em> method handle which is otherwise
1.1188 - * equivalent to the current method handle.
1.1189 - * <p>
1.1190 - * If the current method handle is not of
1.1191 - * {@linkplain #asVarargsCollector variable arity},
1.1192 - * the current method handle is returned.
1.1193 - * This is true even if the current method handle
1.1194 - * could not be a valid input to {@code asVarargsCollector}.
1.1195 - * <p>
1.1196 - * Otherwise, the resulting fixed-arity method handle has the same
1.1197 - * type and behavior of the current method handle,
1.1198 - * except that {@link #isVarargsCollector isVarargsCollector}
1.1199 - * will be false.
1.1200 - * The fixed-arity method handle may (or may not) be the
1.1201 - * a previous argument to {@code asVarargsCollector}.
1.1202 - * <p>
1.1203 - * Here is an example, of a list-making variable arity method handle:
1.1204 - * <blockquote><pre>{@code
1.1205 -MethodHandle asListVar = publicLookup()
1.1206 - .findStatic(Arrays.class, "asList", methodType(List.class, Object[].class))
1.1207 - .asVarargsCollector(Object[].class);
1.1208 -MethodHandle asListFix = asListVar.asFixedArity();
1.1209 -assertEquals("[1]", asListVar.invoke(1).toString());
1.1210 -Exception caught = null;
1.1211 -try { asListFix.invoke((Object)1); }
1.1212 -catch (Exception ex) { caught = ex; }
1.1213 -assert(caught instanceof ClassCastException);
1.1214 -assertEquals("[two, too]", asListVar.invoke("two", "too").toString());
1.1215 -try { asListFix.invoke("two", "too"); }
1.1216 -catch (Exception ex) { caught = ex; }
1.1217 -assert(caught instanceof WrongMethodTypeException);
1.1218 -Object[] argv = { "three", "thee", "tee" };
1.1219 -assertEquals("[three, thee, tee]", asListVar.invoke(argv).toString());
1.1220 -assertEquals("[three, thee, tee]", asListFix.invoke(argv).toString());
1.1221 -assertEquals(1, ((List) asListVar.invoke((Object)argv)).size());
1.1222 -assertEquals("[three, thee, tee]", asListFix.invoke((Object)argv).toString());
1.1223 - * }</pre></blockquote>
1.1224 - *
1.1225 - * @return a new method handle which accepts only a fixed number of arguments
1.1226 - * @see #asVarargsCollector
1.1227 - * @see #isVarargsCollector
1.1228 - */
1.1229 - public MethodHandle asFixedArity() {
1.1230 - assert(!isVarargsCollector());
1.1231 - return this;
1.1232 - }
1.1233 -
1.1234 - /**
1.1235 - * Binds a value {@code x} to the first argument of a method handle, without invoking it.
1.1236 - * The new method handle adapts, as its <i>target</i>,
1.1237 - * the current method handle by binding it to the given argument.
1.1238 - * The type of the bound handle will be
1.1239 - * the same as the type of the target, except that a single leading
1.1240 - * reference parameter will be omitted.
1.1241 - * <p>
1.1242 - * When called, the bound handle inserts the given value {@code x}
1.1243 - * as a new leading argument to the target. The other arguments are
1.1244 - * also passed unchanged.
1.1245 - * What the target eventually returns is returned unchanged by the bound handle.
1.1246 - * <p>
1.1247 - * The reference {@code x} must be convertible to the first parameter
1.1248 - * type of the target.
1.1249 - * <p>
1.1250 - * (<em>Note:</em> Because method handles are immutable, the target method handle
1.1251 - * retains its original type and behavior.)
1.1252 - * @param x the value to bind to the first argument of the target
1.1253 - * @return a new method handle which prepends the given value to the incoming
1.1254 - * argument list, before calling the original method handle
1.1255 - * @throws IllegalArgumentException if the target does not have a
1.1256 - * leading parameter type that is a reference type
1.1257 - * @throws ClassCastException if {@code x} cannot be converted
1.1258 - * to the leading parameter type of the target
1.1259 - * @see MethodHandles#insertArguments
1.1260 - */
1.1261 - public MethodHandle bindTo(Object x) {
1.1262 - Class<?> ptype;
1.1263 - @SuppressWarnings("LocalVariableHidesMemberVariable")
1.1264 - MethodType type = type();
1.1265 - if (type.parameterCount() == 0 ||
1.1266 - (ptype = type.parameterType(0)).isPrimitive())
1.1267 - throw newIllegalArgumentException("no leading reference parameter", x);
1.1268 - x = ptype.cast(x); // throw CCE if needed
1.1269 - return bindReceiver(x);
1.1270 - }
1.1271 -
1.1272 - /**
1.1273 - * Returns a string representation of the method handle,
1.1274 - * starting with the string {@code "MethodHandle"} and
1.1275 - * ending with the string representation of the method handle's type.
1.1276 - * In other words, this method returns a string equal to the value of:
1.1277 - * <blockquote><pre>{@code
1.1278 - * "MethodHandle" + type().toString()
1.1279 - * }</pre></blockquote>
1.1280 - * <p>
1.1281 - * (<em>Note:</em> Future releases of this API may add further information
1.1282 - * to the string representation.
1.1283 - * Therefore, the present syntax should not be parsed by applications.)
1.1284 - *
1.1285 - * @return a string representation of the method handle
1.1286 - */
1.1287 - @Override
1.1288 - public String toString() {
1.1289 - if (DEBUG_METHOD_HANDLE_NAMES) return debugString();
1.1290 - return standardString();
1.1291 - }
1.1292 - String standardString() {
1.1293 - return "MethodHandle"+type;
1.1294 - }
1.1295 - String debugString() {
1.1296 - return standardString()+"/LF="+internalForm()+internalProperties();
1.1297 - }
1.1298 -
1.1299 - //// Implementation methods.
1.1300 - //// Sub-classes can override these default implementations.
1.1301 - //// All these methods assume arguments are already validated.
1.1302 -
1.1303 - // Other transforms to do: convert, explicitCast, permute, drop, filter, fold, GWT, catch
1.1304 -
1.1305 - /*non-public*/
1.1306 - MethodHandle setVarargs(MemberName member) throws IllegalAccessException {
1.1307 - if (!member.isVarargs()) return this;
1.1308 - int argc = type().parameterCount();
1.1309 - if (argc != 0) {
1.1310 - Class<?> arrayType = type().parameterType(argc-1);
1.1311 - if (arrayType.isArray()) {
1.1312 - return MethodHandleImpl.makeVarargsCollector(this, arrayType);
1.1313 - }
1.1314 - }
1.1315 - throw member.makeAccessException("cannot make variable arity", null);
1.1316 - }
1.1317 - /*non-public*/
1.1318 - MethodHandle viewAsType(MethodType newType) {
1.1319 - // No actual conversions, just a new view of the same method.
1.1320 - return MethodHandleImpl.makePairwiseConvert(this, newType, 0);
1.1321 - }
1.1322 -
1.1323 - // Decoding
1.1324 -
1.1325 - /*non-public*/
1.1326 - LambdaForm internalForm() {
1.1327 - return form;
1.1328 - }
1.1329 -
1.1330 - /*non-public*/
1.1331 - MemberName internalMemberName() {
1.1332 - return null; // DMH returns DMH.member
1.1333 - }
1.1334 -
1.1335 - /*non-public*/
1.1336 - Class<?> internalCallerClass() {
1.1337 - return null; // caller-bound MH for @CallerSensitive method returns caller
1.1338 - }
1.1339 -
1.1340 - /*non-public*/
1.1341 - MethodHandle withInternalMemberName(MemberName member) {
1.1342 - if (member != null) {
1.1343 - return MethodHandleImpl.makeWrappedMember(this, member);
1.1344 - } else if (internalMemberName() == null) {
1.1345 - // The required internaMemberName is null, and this MH (like most) doesn't have one.
1.1346 - return this;
1.1347 - } else {
1.1348 - // The following case is rare. Mask the internalMemberName by wrapping the MH in a BMH.
1.1349 - MethodHandle result = rebind();
1.1350 - assert (result.internalMemberName() == null);
1.1351 - return result;
1.1352 - }
1.1353 - }
1.1354 -
1.1355 - /*non-public*/
1.1356 - boolean isInvokeSpecial() {
1.1357 - return false; // DMH.Special returns true
1.1358 - }
1.1359 -
1.1360 - /*non-public*/
1.1361 - Object internalValues() {
1.1362 - return null;
1.1363 - }
1.1364 -
1.1365 - /*non-public*/
1.1366 - Object internalProperties() {
1.1367 - // Override to something like "/FOO=bar"
1.1368 - return "";
1.1369 - }
1.1370 -
1.1371 - //// Method handle implementation methods.
1.1372 - //// Sub-classes can override these default implementations.
1.1373 - //// All these methods assume arguments are already validated.
1.1374 -
1.1375 - /*non-public*/ MethodHandle convertArguments(MethodType newType) {
1.1376 - // Override this if it can be improved.
1.1377 - return MethodHandleImpl.makePairwiseConvert(this, newType, 1);
1.1378 - }
1.1379 -
1.1380 - /*non-public*/
1.1381 - MethodHandle bindArgument(int pos, char basicType, Object value) {
1.1382 - // Override this if it can be improved.
1.1383 - return rebind().bindArgument(pos, basicType, value);
1.1384 - }
1.1385 -
1.1386 - /*non-public*/
1.1387 - MethodHandle bindReceiver(Object receiver) {
1.1388 - // Override this if it can be improved.
1.1389 - return bindArgument(0, 'L', receiver);
1.1390 - }
1.1391 -
1.1392 - /*non-public*/
1.1393 - MethodHandle bindImmediate(int pos, char basicType, Object value) {
1.1394 - // Bind an immediate value to a position in the arguments.
1.1395 - // This means, elide the respective argument,
1.1396 - // and replace all references to it in NamedFunction args with the specified value.
1.1397 -
1.1398 - // CURRENT RESTRICTIONS
1.1399 - // * only for pos 0 and UNSAFE (position is adjusted in MHImpl to make API usable for others)
1.1400 -// assert pos == 0 && basicType == 'L' && value instanceof Unsafe;
1.1401 - MethodType type2 = type.dropParameterTypes(pos, pos + 1); // adjustment: ignore receiver!
1.1402 - LambdaForm form2 = form.bindImmediate(pos + 1, basicType, value); // adjust pos to form-relative pos
1.1403 - return copyWith(type2, form2);
1.1404 - }
1.1405 -
1.1406 - /*non-public*/
1.1407 - MethodHandle copyWith(MethodType mt, LambdaForm lf) {
1.1408 - throw new InternalError("copyWith: " + this.getClass());
1.1409 - }
1.1410 -
1.1411 - /*non-public*/
1.1412 - MethodHandle dropArguments(MethodType srcType, int pos, int drops) {
1.1413 - // Override this if it can be improved.
1.1414 - return rebind().dropArguments(srcType, pos, drops);
1.1415 - }
1.1416 -
1.1417 - /*non-public*/
1.1418 - MethodHandle permuteArguments(MethodType newType, int[] reorder) {
1.1419 - // Override this if it can be improved.
1.1420 - return rebind().permuteArguments(newType, reorder);
1.1421 - }
1.1422 -
1.1423 - /*non-public*/
1.1424 - MethodHandle rebind() {
1.1425 - // Bind 'this' into a new invoker, of the known class BMH.
1.1426 - MethodType type2 = type();
1.1427 - LambdaForm form2 = reinvokerForm(this);
1.1428 - // form2 = lambda (bmh, arg*) { thismh = bmh[0]; invokeBasic(thismh, arg*) }
1.1429 - return BoundMethodHandle.bindSingle(type2, form2, this);
1.1430 - }
1.1431 -
1.1432 - /*non-public*/
1.1433 - MethodHandle reinvokerTarget() {
1.1434 - throw new InternalError("not a reinvoker MH: "+this.getClass().getName()+": "+this);
1.1435 - }
1.1436 -
1.1437 - /** Create a LF which simply reinvokes a target of the given basic type.
1.1438 - * The target MH must override {@link #reinvokerTarget} to provide the target.
1.1439 - */
1.1440 - static LambdaForm reinvokerForm(MethodHandle target) {
1.1441 - MethodType mtype = target.type().basicType();
1.1442 - LambdaForm reinvoker = mtype.form().cachedLambdaForm(MethodTypeForm.LF_REINVOKE);
1.1443 - if (reinvoker != null) return reinvoker;
1.1444 - if (mtype.parameterSlotCount() >= MethodType.MAX_MH_ARITY)
1.1445 - return makeReinvokerForm(target.type(), target); // cannot cache this
1.1446 - reinvoker = makeReinvokerForm(mtype, null);
1.1447 - return mtype.form().setCachedLambdaForm(MethodTypeForm.LF_REINVOKE, reinvoker);
1.1448 - }
1.1449 - private static LambdaForm makeReinvokerForm(MethodType mtype, MethodHandle customTargetOrNull) {
1.1450 - boolean customized = (customTargetOrNull != null);
1.1451 - MethodHandle MH_invokeBasic = customized ? null : MethodHandles.basicInvoker(mtype);
1.1452 - final int THIS_BMH = 0;
1.1453 - final int ARG_BASE = 1;
1.1454 - final int ARG_LIMIT = ARG_BASE + mtype.parameterCount();
1.1455 - int nameCursor = ARG_LIMIT;
1.1456 - final int NEXT_MH = customized ? -1 : nameCursor++;
1.1457 - final int REINVOKE = nameCursor++;
1.1458 - LambdaForm.Name[] names = LambdaForm.arguments(nameCursor - ARG_LIMIT, mtype.invokerType());
1.1459 - Object[] targetArgs;
1.1460 - MethodHandle targetMH;
1.1461 - if (customized) {
1.1462 - targetArgs = Arrays.copyOfRange(names, ARG_BASE, ARG_LIMIT, Object[].class);
1.1463 - targetMH = customTargetOrNull;
1.1464 - } else {
1.1465 - names[NEXT_MH] = new LambdaForm.Name(NF_reinvokerTarget, names[THIS_BMH]);
1.1466 - targetArgs = Arrays.copyOfRange(names, THIS_BMH, ARG_LIMIT, Object[].class);
1.1467 - targetArgs[0] = names[NEXT_MH]; // overwrite this MH with next MH
1.1468 - targetMH = MethodHandles.basicInvoker(mtype);
1.1469 - }
1.1470 - names[REINVOKE] = new LambdaForm.Name(targetMH, targetArgs);
1.1471 - return new LambdaForm("BMH.reinvoke", ARG_LIMIT, names);
1.1472 - }
1.1473 -
1.1474 - private static final LambdaForm.NamedFunction NF_reinvokerTarget;
1.1475 - static {
1.1476 - try {
1.1477 - NF_reinvokerTarget = new LambdaForm.NamedFunction(MethodHandle.class
1.1478 - .getDeclaredMethod("reinvokerTarget"));
1.1479 - } catch (ReflectiveOperationException ex) {
1.1480 - throw newInternalError(ex);
1.1481 - }
1.1482 - }
1.1483 -
1.1484 - /**
1.1485 - * Replace the old lambda form of this method handle with a new one.
1.1486 - * The new one must be functionally equivalent to the old one.
1.1487 - * Threads may continue running the old form indefinitely,
1.1488 - * but it is likely that the new one will be preferred for new executions.
1.1489 - * Use with discretion.
1.1490 - */
1.1491 - /*non-public*/
1.1492 - void updateForm(LambdaForm newForm) {
1.1493 - if (form == newForm) return;
1.1494 - this.form = newForm;
1.1495 - this.form.prepare(); // as in MethodHandle.<init>
1.1496 - }
1.1497 -}